Abstract
Using chemical mutagenesis, mutants of Hansenula polymorpha that were defective in fatty acid synthesis were selected based on their growth requirements on saturated fatty acid mixtures. One mutant (S7) was incapable of synthesizing polyunsaturated fatty acids (PUFA), linoleic and α-linolenic acids. A genetic analysis demonstrated that the S7 strain had a double lesion affecting fatty acid synthesis and Δ(12)-desaturation. A segregant with a defect in PUFA synthesis (H69-2C) displayed normal growth characteristics in the temperature range of 20-42°C through a modulation of the cellular fatty acid composition. Compared with the parental strain, this yeast mutant had increased sensitivity at low and high temperatures (15 and 48°C, respectively) with an increased tolerance to oxidative stress. The responses to ethanol stress were similar for the parental and PUFA-defective strains. Myristic acid was also determined to play an essential role in the cell growth of H. polymorpha. These findings suggest that both the type of cellular fatty acids and the composition of fatty acids might be involved in the stress responsive mechanisms in this industrially important yeast.
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